COULOMB. 



301 



Coulomb, "by difference of temperature. He found that it dimi- 

 """""" /"*"*'' rushes as the temperature is increased ; and with the as- 

 sistance of a theorem by M. Laplace, he found that a 

 magnetic needle must acquire a temperature of 700° of 

 the centigrade scale, before it is entirely deprived of its 

 magnetism. It had long been believed that iron was 

 the only body that possessed the magnetic virtue, but 

 Coulomb found unequivocal marks of attraction in almost 

 all bodies that he tried; and hence he concluded, that mag- 

 netism, like electricity, was extended through all nature. 

 This discovery was the last which he made, and his latest 

 moments were employed in verifying it. Several curious 

 experiments have been found among his manuscripts, from 

 which it seems to follow, that if the magnctical attractions, 

 which he discovered in different bodies, were owing to 

 the presence of iron, the quantity of this metal must be' so 

 considerable, that it could not have escaped the notice 

 of chemists. 



The attention of Coulomb having been particularly di- 

 rected to the subject of wind-mills, he published the re- 

 sults of his researches in the Memoirs of the Academy 

 for 1781, under the title of Observations Theoriqucs et 

 Experimentales sur I'effet de Moulins a vent, et sur le 

 figure de leurs ailes. These experiments were made upon 

 more than fifty wind-mills in the neighbourhood of Lisle. 

 He found that almost all of them performed near! 3' the 

 same quantity of work when the wind moved with the 

 velocity of 18 or 20 feet per second, and from this. he 

 justly concluded, that the parts of these machines must 

 have been so adjusted as to produce nearly a maximum 

 effect. 



In the latter part of his life, Coulomb was appointed 

 commissary to the king in Bretagne, and was sent by the 

 minister of the Marine to examine the canals and public 

 works in that province. On this occasion, it required 

 all the energy of his character to stop the ruinous pro- 

 jects which had been on the eve of execution ; and the 

 province, out of gratitude for his services, rewarded 

 him with a very considerable present. 



At the commencement of the revolution, Coulomb re- 

 signed almost all his offices, and particularly the general 

 superintendance of the fountains of France, which had 

 been hereditary in his family, and which he had hoped 

 to transmit to his children. He employed himself in 

 collecting the wrecks of his fortune ; and expected to 

 find, in the continuance of his scientific labours, and in 

 his correspondence with the Academy, that happiness of 

 which external circumstances could not deprive him. The 

 Academy, however, was suppressed, and his situation as 

 member of the Commission of Weights and Measures was 

 taken from him. He was soon after compelled to leave 

 Paris, by the edict which expelled all the nobles; and 

 he retired with his friend the Chevalier Borda to a small 

 estate which he possessed near Blois. In this retreat, 

 he pursued, in the bosom of his family, those studies 

 which had in better times occupied his mind. His at- 

 tention was accidentally directed to the subject of ve- 

 getation, and he made some experiments on the mo- 

 tion of the sap, of which he has given a short ac- 

 count in a paper published in the Memoirs of the Na- 

 tional Institute, torn ii. p. 24-6, under the title of Expe- 

 riences relatives a la circulation de la seve dans les arbres. 

 The result of these experiments, which is however pro- 

 posed merely as a conjecture, is, that the circulation of 



the sap in vegetables is carried on by the parts adjoining CouIomiS. 

 to the central canal of the tree, and by the infinity of *""" "V"""' 

 medullary horizontal radii, which form a communication 

 with the axis of the plant. 



In the year 1798* Coulomb read to the national Insti- 

 tute a long and valuable paper, entitled Resullal de pln- 

 sieurs experiences destine es a determiner la quant ite d 'ac- 

 tion que les hommes peuvent J'ournir par leur travail jour- 

 nalier, suivant les differentes manieres dont Us emploient 

 leurs forces. In this elaborate paper, which consists of 

 thirty sections, the object of the author is to determine 

 how much loads of different magnitudes may diminish 

 the quantity of action which a man can furnish in a day ; 

 and the experiments which were emploj'cd for this purpose, 

 were made upon the most natural and ordinary motions 

 of men, such as walking horizontally, or mounting a lad- 

 der. He found, that the load which a man ascending 

 stairs should carry, in order to produce the greatest useful 

 effect, is 173.8 pounds avoirdupois, on the supposition, 

 that he is to continue the exertion during a whole da}'. 

 In this case, the quantity of action which the labourer ex- 

 erts is 183.C6 pounds avoirdupois, raised through 3282 

 feet. Coulomb then proceeds to compare the total quan- 

 tity of action which a man can furnish when ascending 

 steps, with that which he exerts in driving a winch, in 

 digging the ground, in pulling a rope horizontally, and in 

 walking on a level road ; and the general results of these 

 comparisons, give quantities of action much less consi- 

 derable than those which had been employed by all pre- 

 ceding authors in their calculations of machines. Cou- 

 lomb also found, that the mean quantity of action de- 

 pended greatly on the food, as well as on the climate ; 

 and that in warm climates, such as Martinique, where the 

 labourer is almost always inundated with perspiration, 

 the quantity of action furnished by one man is scarcely 

 one-half of that which is furrushed in France. 



The subject of magnetism continued to occupy the 

 thoughts of Coulomb, and he produced a very valuable 

 paper in 1800, which was published in the Memoirs of 

 the Institute, torn. iii. under the title of Determination 

 Thcorique et Experimcntale des Forces qui ramenevt dif- 

 Jerents aiguilles aimantces a saturation, a leur meridicn 

 magnelique. 



In the same volume of the Memoirs of the Institute, 

 he published one of the most curious of all his papers 

 on the cohesion of fluids It is entitled, Experiences 

 destinies a determiner la coherence des jluides et les 

 lois de leur resistance dans les mouvements ties lents. In 

 these experiments, Coulomb employed the principle of 

 torsion, for determining the cohesion of fluids, and the 

 laws of their resistance, in very slow motions. Newton, 

 D Bernoulli, and Gravesende, represent the resistance 

 which a fluid at rest opposes to a body in motion, by a 

 formula of two terms, one of which is as the square of 

 the velocity, and the other constant ,• but Coulomb has 

 shewn, by unquestionable experiments, that the resist- 

 ance is represented by two terms, one of which is propor- 

 tional to the simple velocity, and the other to its square, 

 and that, if any constant quantity exists, it is extremely 

 small. He proposed, in a subsequent memoir, to ascer- 

 tain numerically, the part of the resistance which is pro- 

 portional to the single velocity, and to determine the re- 

 sistance of globes, with convex, concave, and plain sur- 

 faces ; but this second memoir was never published. 



